Polyolefin additive composition comprising 3,4-dimethyl dibenzylidene sorbitol and p-methyl dibenzylidene sorbitol

ABSTRACT

A specific combination of two different polyolefin clarifying and nucleating agents, namely 3,4-dimethyldibenzylidene sorbitol and p-methyldibenzylidene sorbitol is provided. Such a combination surprisingly provides improved clarification and crystallization temperatures to polypropylene articles and formulations, better than bis-p-methyldibenzylidene sorbitol alone and equivalent or better than 3,4-dimethyldibenzylidene sorbitol. Such a combination of compounds thus permits the utilization of a new additive for the purpose of modifying polyolefin properties, such as polypropylene clarification and nucleation. The inventive combination may be introduced within any polyolefin composition, again preferably polypropylene, which may then be molded into any shape or form. A method of producing a polyolefin plastic utilizing the inventive combination of compounds is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation of pending application Ser. No.10/461,184 (filed Jun. 13, 2003) which is a divisional of applicationSer. No. 09/785,824 (filed Feb. 16, 2001; granted as U.S. Pat. No.6,586,007).

FIELD OF THE INVENTION

This invention relates to a specific combination of two differentpolyolefin clarifying and nucleating agents, namelybis-3,4-dimethyldibenzylidene sorbitol and bis-p-methyldibenzylidenesorbitol. Such a combination surprisingly provides improvedclarification and crystallization temperatures to polypropylene articlesand formulations, better than bis-p-methyldibenzylidene sorbitol aloneand equivalent or better than 3,4-dimethyldibenzylidene sorbitol alone.Such a combination of compounds thus permits the utilization of a newadditive for the purpose of modifying polyolefin properties, such aspolypropylene clarification and nucleation. The inventive combinationmay be introduced within any polyolefin composition, again preferablypolypropylene, which may then be molded into any shape or form. A methodof producing a polyolefin plastic utilizing the inventive combination ofcompounds is also provided.

BACKGROUND OF THE PRIOR ART

Dibenzylidene sorbitol acetals (“DBS”), substituted DBS, such as can bemade with alkyl substituted aromatic aldehydes, and related acetals havefound utility as nucleating agents, clarifying agents, gelling agents,processing aids, and strength modifiers in polyolefin resins, polyesterresins, deodorant, and antiperspirant compositions; hydrocarbon fuels;waste liquids, especially those containing organic impurities; andpaint.

Such compounds are utilized to provide nucleation sites for polyolefincrystal growth during cooling of a molten formulation. Without beinglimited to one specific scientific theory, it is believed that DBScompounds form fibrous networks within the molten polyolefin (such aspolypropylene) at a temperature well above that required for polyolefincrystal formation. The fibrous networks appear to act as sites for moreordered and faster polyolefin crystallization during cooling. During theprocess of crystallization, polymer crystals organize into largersuperstructures which are referred to as spherulites. The more uniform,and preferably smaller, the spherulite size, the reduced possibility forlight to be scattered. In such a manner, optical opacity of thepolyolefin article itself can be controlled. Thus, DBS compounds arevery important to the polyolefin industry in order to provide suchdesired nucleation and clarification properties.

DBS derivative compounds are typically prepared by the condensationreaction of two moles of an aromatic aldehyde with one mole of apolyhydric alcohol, such as xylitol or sorbitol. Examples of suitableprocesses may be found in Murai et al., U.S. Pat. No. 3,721,682; Muraiet al., U.S. Pat. No. 4,429,140; Machell, U.S. Pat. No. 4,562,265;Kobayashi et al., U.S. Pat. No. 4,902,807; and Scrivens et al., U.S.Pat. No. 5,731,474. All of these references are hereby incorporated byreference in their entirety.

Specific clarifying and nucleating agents for polyolefins includebis-3,4-dimethyldibenzylidene sorbitol (3,4-DMDBS) andbis-p-methyldibenzylidene sorbitol (MDBS). These specific compounds andpolyolefins containing such compounds have been taught previously inU.S. Pat. No. 4,371,645 to Mahaffey and U.S. Pat. No. 5,049,605 toRekers, respectively. Such compounds are thus individually well known aspolyolefin additives and exhibit excellent low haze measurements withinpolyolefins (as low as about 8.0% for 3,4-DMDBS and about 10% for MDBSin random polypropylene copolymer injection molded 50 mil thick plaqueshaving 2000 ppm of clarifier added).

However, there are drawbacks from utilizing MDBS as a clarifying agentsince degradation of such a compound into the benzaldehyde and sorbitolcomponents creates a problem with migration of such benzaldehydes fromthe target polyolefin. In such a situation, foul odors and tastes aregenerated such that the target polyolefin is limited in its end-usefunction to non-food contact applications. To combat this, Milliken &Company developed 3,4-DMDBS. Such a compound appears to suffer from thesame type of degradation possibilities; however, the resultantbenzaldehyde, being 3,4-dimethyl substituted, does not create the sameorganoleptic problems as its p-methylbenzaldehyde counterpart. As aresult, 3,4-DMDBS has become the primary clarifying agent throughout thepolyolefin market.

Unfortunately, though, 3,4-DMDBS is relatively expensive to manufacture.The manufacturing costs required to produce 3,4-DMDBS are above thosefor MDBS. As a result, there remains a great desire to develop a morecost-effective, yet acceptable clarifying agent or composition forpolyolefins which exhibits similar haze results as either of the twocompounds individually. To date, there has been no teaching or fairsuggestion for any such improvements to lower the amount of 3,4-DMDBS inorder to reduce the costs of such a composition solely comprising such apolyolefin clarifying agent without sacrificing clarification ability.There does exist a combination of 3,4-DMDBS withbis(p-chlorobenzylidene) sorbitol in Japanese Application Hei8[1996]-199003 to Kobayashi; however, such a composition providesdeleterious results from an organoleptic perspective. JapaneseApplication Hei 8[1996]-32415, also to Kobayashi, teaches a combinationof MDBS with bis-p-chlorodibenzylidene sorbitol as a polyolefin additiveas well. Again, organoleptics are problematic with such a composition.Neither teaching shows or fairly suggests the combination of 3,4-DMDBSand MDBS. The only other teachings concerning such polyolefin clarifyingcompounds have been as individually utilized compounds within polyolefincompositions and articles, as noted above. Thus, there remains a desireto provide a more cost-effective but similarly performing clarifyingagent comprising the excellent clarifier 3,4-DMDBS.

OBJECTS OF THE INVENTION

Therefore, an object of the invention is to provide a lower costalternative to a polyolefin clarifier containing 3,4-DMDBS aloneexhibiting excellent clarifying capabilities for the same polyolefinarticles and compositions. Another object of the invention is to providea polyolefin composition or article exhibiting a haze measurement ofbelow 10% comprising a clarifying combination of 3,4-DMDBS and MDBS.

Accordingly, this invention encompasses a polyolefin additivecomposition comprising a combination of bothbis(3,4-dimethylbenzylidene) sorbitol and bis(4-methylbenzylidene)sorbitol. More specifically, this invention encompasses such acombination consisting of from 5 to 95% by weight of the totalcombination of bis(3,4-dimethylbenzylidene) sorbitol and from 5 to 95%by weight of the total combination of bis(4-methylbenzylidene) sorbitol.Finished solid articles of polyolefins, such as, preferably, though notnecessarily, polypropylene, comprising such an additive composition arealso contemplated within this invention. Furthermore, such an inventionis also defined and thus encompasses a polyolefin nucleator compositioncomprising at least 1000 ppm of a mixture of compounds, wherein saidcompounds are bis(3,4-dimethylbenzylidene) sorbitol andbis(p-methylbenzylidene) sorbitol, wherein said polyolefin nucleatorcomposition provides a crystallization onset temperature within a targetpolyolefin article formulation above the crystallization onsettemperature provided for a comparative polyolefin article comprising thesame polyolefin formulation but comprising bis(p-methylbenzylidene)sorbitol as its sole polyolefin nucleator component, wherein theconcentration of said sole polyolefin nucleator component within saidcomparative polyolefin article is equivalent to the total concentrationof the polyolefin nucleator mixture within said target polyolefinarticle. Also contemplated is a polyolefin nucleator compositioncomprising at least 1000 ppm of a combination of compounds, wherein saidcompounds are bis(3,4-dimethylbenzylidene) sorbitol andbis(p-methylbenzylidene) sorbitol, wherein said polyolefin nucleatorcomposition provides a peak crystallization temperature within a targetpolyolefin article formulation above the peak crystallizationtemperature provided for a comparative polyolefin article comprising thesame polyolefin formulation but comprising bis(p-methylbenzylidene)sorbitol as its sole polyolefin nucleator component, wherein theconcentration of said sole polyolefin nucleator component within saidcomparative polyolefin article is equivalent to the total concentrationof the polyolefin nucleator mixture within said target polyolefinarticle. Further contemplated is a polyolefin clarifier compositioncomprising at least 1000 ppm of a combination of nucleator compounds,wherein said compounds are bis(3,4dimethylbenzylidene) sorbitol andbis(p-methylbenzylidene) sorbitol, wherein said polyolefin clarifiercomposition provides a haze measurement within a target polyolefinarticle formulation below the haze measurement provided for acomparative polyolefin article comprising the same polyolefinformulation but comprising bis(p-methylbenzylidene) sorbitol as its solepolyolefin clarifier component, wherein such haze measurements are madein accordance with ASTM Standard Test Method D1003-61, and wherein theconcentration of said sole polyolefin nucleator component within saidcomparative polyolefin article is equivalent to the total concentrationof the polyolefin nucleator mixture within said target polyolefinarticle. The importance of and definitions of such crystallization onsettemperatures, peak crystallization temperatures, and haze measurementsare discussed in greater detail below. Lastly, the invention encompassesa method of nucleating a polyolefin comprising the steps of (a)providing a nucleator composition comprising at least 1000 ppm of acombination of bis(3,4-dimethylbenzylidene) sorbitol andbis(4-methylbenzylidene) sorbitol; (b) providing a polyolefinformulation; (c) mixing said composition of step “a” with the polyolefinof step “b”; (d) melting said resultant mixture of step “c”; andallowing said molten mixture of step “d” to cool. Nowhere within thepertinent prior art is such a combination, polyolefin additivecomposition, polyolefin articles comprising such combinations andadditives compositions, or methods of producing polyolefin articlestaught or fairly suggested.

DETAILED DESCRIPTION OF THE INVENTION

The invention thus comprises basically both 3,4-DMDBS and MDBS inspecific proportions. The combination of both compounds has been avoidedin the past, as noted above, due to the difficulties in utilizing MDBSin a large range of applications and end-uses. Without the apparentability to provide an acceptable clarifier composition including such acompound, the possibility of servicing only a limited market ofend-users has thwarted widespread attempts of incorporating such acompound within different clarifying formulations. Without the desire orneed to investigate the effects of such an inventive combination ofcompounds within a polyolefin clarifying formulation, production andanalyses of such potential mixtures have been deemphasized.

However, with the need to provide lower cost alternatives to 3,4-DMDBSalone, as well as the availability of certain types of compounds toprevent MDBS degradation, neutralize degrading acids and other oxidants,and/or compounds which scavenge free degraded benzaldehyde, all withinthe target polyolefin, the potential for avoiding the aforementioneddifficulties with organoleptic issues may potentially permit morewidespread use of MDBS within a broader market of end-uses, particularlynon-food contact applications. Such potential organoleptic improvementsfor MDBS containing polyolefins is rather limited, however, since thenecessity of scavenging large amounts of degraded benzaldehydes requiresthe presence of an appreciable amount of extra solids within the targetpolyolefin itself. Such an addition is problematic since the increase insolids within the target polyolefin invariably affects the clarity andcost of the target formulation. Thus, polyolefins comprising all MDBSare still problematic on a widespread basis due to the difficulties inreducing haze and organoleptic problems simultaneously with suchclarifying compounds. Hence, the development of the inventivecombination of 3,4-DMDBS and MDBS as a synergistically active clarifyingagent is of great importance within the clarified polyolefin industry.

As noted above, surprisingly, it has now been found that such a mixtureof clarifiers exhibits a synergistic clarifying effect in polyolefin. Asnoted in TABLE 2, below, for random copolymer (RCP), for example, about2000 ppm of 3,4-DMDBS provides a haze measurement of about 8% and MDBSat 2000 ppm of about 10% (all within, as one example, 50 mil plaques ofinjection molded RCP). By mixing the two compounds, for example, toabout 1500 ppm 3,4-DMDBS and about 500 ppm MDBS, the resultant hazemeasurement is about 8.4% (much lower than for MDBS alone). Furthermore,a mixture of about 1600 ppm MDBS with about 400 ppm 3,4-DMDBS provides ahaze measurement of about 7.9%. Thus, even though MDBS exhibits anappreciably higher haze measurement than 3,4-DMDBS, surprisingly thecombination of the two different compounds provides a comparable hazeresult for 3,4-DMDBS alone.

Such a result is against commonly accepted practice. For example, asnoted above, and without intending to be bound to any specificscientific theory, it appears that the DBS compound within a polyolefinappears to provide a fibrous network of nucleation sites for polyolefincrystal growth during cooling of the molten polymer. The network formedby 3,4-DMDBS alone accords what appears to be standard small spherulitesizes for low haze measurements. The network formed by MDBS produceslarger average spherulite sizes, thereby producing high hazemeasurements. It is noted that all haze measurements noted hereininclude a standard deviation of +/−0.25 haze units.

Although haze is an important measurement to determine the effectivenessof certain clarifying agents, other characteristics exhibited by suchagents, and transferred to the final polyolefin product are of greatinterest as well. For instance, crystallization is important in order todetermine the time needed to form a solid from the molten polyolefin/DBScomposition. The rate of crystallization is typically quantified byreporting the onset crystallization temperature, which defines thebeginning of the crystallization process, and the peak crystallizationtemperature, which defines the temperature where the crystallizationrate is highest. Both the onset crystallization temperature and the peakcrystallization temperature are indicative of the crystallizationprocess occurring in a polymer sample. In order to reduce the amount oftime needed to form the final product, as well as to provide the mosteffective nucleation for the polyolefin, the best DBS compounds addedwill most likely, though not necessarily, also provide the highest peakcrystallization temperature and the highest onset crystallizationtemperature.

The crystallization temperature exhibited by 3,4-DMDBS in RCP, forexample, is greater than an entire degree above that for MDBS in RCP(114.1° C. to 112.9° C.). Thus, without intending to be bound to anyspecific scientific theory, it appears that the polypropylene crystalsform more readily and quickly with 3,4-DMDBS due to the highercrystallization temperature exhibited thereby. However, (in the mixedsystems) the addition of amounts of 3,4-DMDBS appear not only not toreduce the haze results from MDBS alone, but also increase both the peakcrystallization and onset crystallization temperatures. It would beexpected that the arrangement of polyolefin crystals would be morehaphazard with a mixed clarifier system since the fibrous networksformed by the initial 3,4-DMDBS would seemingly produce differentspherulite size crystals of polyolefin than would the MDBS network.Again, this appears not to be the case in this instance. The similarityin haze results to 3,4-DMDBS alone suggests that the polyolefin crystalgrowth remains uniform in effect. Such results are, again, highlyunexpected in view of common understandings of nucleated and clarifiedpolyolefins.

A similar phenomenom occurs with regard to the aforementionedcrystallization onset temperatures. MDBS exhibits, in RCP, acrystallization onset temperature of about 117.1° C. at 2000 ppm, and3,4-DMDBS exhibits, also in RCP at 2000 ppm, a crystallization onsettemperature of about 118.6° C. With a combination of these twoadditives, the crystallization onset temperature is increased,surprisingly, to a level as high as almost 119° C. All crystallizationand onset temperatures listed herein include a statistical error of+/−0.1° C.

Thus, it has been found that a composition of from 5-95% by weight ofMDBS and from 5-95% by weight of 3,4-DMDBS, with a total of 100% forboth components, provides the highly unexpected benefits as noted above,particularly when incorporated within a target polyolefin, preferablypolypropylene. Preferably, such a mixture is from about 10-90% by weightMDBS and from about 10-90% by weight of 3,4-DMDBS; more preferably,about 20-90% by weight of MDBS and from about 10-80% by weight of3,4-DMDBS; still more preferably, 25-90% MDBS, and 10-75% 3,4-DMDBS, andmost preferably about 50-80% MDBS and about 20-50% 3,4-DMDBS. Such acombination may be incorporated within an additives package compositionincluding other components, including, base polyolefin, and othercompounds and formulations noted below in greater detail. Such aninventive combination, and compositions comprising such an inventivecombination, may be present in any type of standard polyolefin additiveform, including, without limitation, powder, prill, agglomerate, liquidsuspension, and the like. Basically, any form may be exhibited by such acombination or composition including such combination made fromblending, agglomeration, compaction, and/or extrusion. The totalconcentration of the inventive combination of nucleator compounds withinthe target polyolefin may be anywhere from about 1000 ppm to about 4000ppm; preferably such a concentration is from about 1000 ppm to about3500 ppm; more preferably is from about 1200 ppm to about 3000 ppm;still more preferably is from about 1500 ppm to about 3000 ppm; and mostpreferably from about 1500 ppm to about 2200 ppm.

Optional additives within the base composition comprising this inventivemixture may include plasticizers, antistatic agents, stabilizers,ultraviolet absorbers, and other similar standard polyolefinthermoplastic additives. Other additives may also be present within thiscomposition, most notably antioxidants, antistatic compounds, perfumes,acid netutralizers, and the like. In particular, it is contemplated thatcertain organoleptic improvement additives be added for the purpose ofpermitting increased amounts of MDBS to be incorporated within theinventive combination, compositions thereof, and end-product polyolefincomprising such. The term “organoleptic improvement additive” isintended to encompass such compounds and formulations as antioxidants(to prevent degradation of both the polyolefin and possibly the targetMDBS and/or 3,4-DMDBS), acid neutralizers (to prevent the ability ofappreciable amounts of residual acids from attacking the DBS compounds),and benzaldehyde scavengers (such as hydrazides, hydrazines, and thelike, to prevent the migration of foul tasting and smellingbenzaldehydes to the target polyolefin surface). Such compounds andformulations can be added in any amounts in order to provide suchorganoleptic improvements as needed. However, the amounts should notappreciably affect the haze results for the target polyolefin itself.Thus, lower amounts on the order of from about 20 ppm to about 2,000 ppmof the total polyolefin component are desired.

The term polyolefin or polyolefin resin is intended to encompass anymaterials comprised of at least one polyolefin compound. Preferredexamples include polypropylene, polyethylene, polybutylene, and anyblends or copolymers thereof, whether high or low density incomposition. The term thermoplastic is well known in the art to mean apolymeric material which will melt upon exposure to sufficient heat butwill retain its solidified state, but not prior shape (without use of amold), upon sufficient cooling. The nucleated polyolefin is intended tobe utilized as, for instance and not by limitation, medical devices,such as syringes, intravenous supply containers, and blood collectionapparati; pipes and tubes; standard storage containers; food packages;liquid containers, such as for drinks, medicines, shampoos, and thelike; apparel cases; microwaveable articles; shelves; cabinet doors;mechanical parts; automobile parts; and any article where the effects ofnucleation may be advantageous.

The inventive nucleator and/or clarifier compositions are also definedin terms of their ability to provide improved crystallization onsettemperatures, peak crystallization temperatures, and haze measurementswithin polyolefin article formulations above such quantifiableproperties available through the sole utilization ofbis(p-methylbenzylidene) sorbitol as a nucleator and/or clarifier withinthe same polyolefin article formulation and at the same totalconcentration as the inventive nucleator combination, as noted above.The term “same polyolefin article formulation” in this context intendedto define the same base polyolefin content as used to produce thecomparable polyolefin articles with the inventive compositionsincorporated therein, including the same manufacturing processparameters (e.g., melting temperatures, molder barrel temperatures,cooling rates and temperatures, and the like). It would be wellappreciated by the ordinarily skilled artisan that such a term does notconnote the same exact polyolefin article itself. Thus, in comparisonwith standard polyolefin article formulations of the same base poyolefincontent but with bis(p-methylbenzylidene) sorbitol as the solenucleating/clarifying additive, the inventive compositions provideincreased crystallization onset temperatures and peak crystallizationtemperatures and decreased haze measurements where the concentration ofthe sole polyolefin nucleator component a comparative polyolefin articleis equivalent to the total concentration of the polyolefin nucleatormixture within the inventive target polyolefin article.

PREFERRED EMBODIMENTS OF THE INVENTION

Examples of particularly preferred additive compositions comprisingmixtures of 3,4-DMDBS and MDBS as well as polyolefin articles comprisingsuch mixtures are presented below.

Production of Inventive DBS Mixtures

The specific DBS mixtures were comprised of powders of the individualDBS compounds which were then mixed together physically in powder formin the proportions listed below. DBS, itself, indicates dibenzylidenesorbitol; EDBS indicates bis(p-ethylbenzylidene) sorbitol; and TDBSindicates 1,3;2,4-bis(5′, 6′, 7′,8′-tetrahydro-2-naphthylidene)sorbitol. TABLE 1 Proportions Of Inventive DBS Mixtures 3,4-DMDBS MDBSDBS EDBS TDBS (ppm) (ppm) (ppm) (ppm) (ppm) Ex.  1 1750 250 0 0 0  21500 500 0 0 0  3 1250 750 0 0 0  4 1000 1000 0 0 0  5 750 1250 0 0 0  6600 1400 0 0 0  7 500 1500 0 0 0  8 400 1600 0 0 0  9 300 1700 0 0 0 10250 1750 0 0 0 11 200 1800 0 0 0 12 100 1900 0 0 0 13 1250 1250 0 0 0(Comparatives) 14 2000 0 0 0 0 15 0 2000 0 0 0 16 1000 0 1000 0 0 17 5000 1500 0 0 18 0 0 2000 0 0 19 1000 0 0 1000 0 20 400 0 0 1600 0 21 0 0 02000 0 22 0 1250 0 0 1250 23 0 0 0 0 2500 24 2500 0 0 0 0 25 0 2500 0 00Production of Clarified Polypropylene with the Inventive DBS Mixtures

One kilogram batches of target polypropylene were produced in accordancewith the owing table: POLYPROPYLENE COMPOSITION TABLE Component AmountPolypropylene random copolymer flake (3% ethylene) 1,000 g Irganox ®1010, Primary Antioxidant (from Ciba)   500 ppm Irgafos ® 168, SecondaryAntioxidant (from Ciba)  1000 ppm Calcium Stearate, Acid Scavenger   800ppm Clarifying compounds or compositions as noted

The base resin (random copolymer, hereinafter “RCP”) and all additiveswere weighed and then blended in a Welex high-intensity mixer for 1minute at about 1600 rpm. All samples were then melt compounded on aKillion single screw extruder at a ramped temperature from about 204° to232° C. through four heating zones. The melt temperature upon exit ofthe extruder die was about 246° C. The screw had a diameter of 2.54 cmand a length/diameter ratio of 24:1. Upon melting the molten polymer wasfiltered through a 60 mesh (250 micron) screen. Plaques of the targetpolypropylene were then made on an Arburg 25 ton injection molder. Themolder barrel was set at a temperature of 220° C. The plaques haddimensions of about 51 mm×76 mm×1.27 mm made from a mirror-polished mold(SPI 1). The mold cooling circulating water was controlled at atemperature of 25° C. After allowing the plaques to age for 24 hours atroom temperature, haze values were measured according to ASTM StandardTest Method D1003-61 “Standard Test Method for Haze and LuminousTransmittance of Transparent Plastics” using a BYK Gardner HazegardPlus.

A Perkin-Elmer DSC7 calibrated with indium was used to measure the peakcrystallization temperature and the onset crystallization temperature ofthe polymer. The specific polyolefin/DBS mixture composition was heatedfrom 60° C. to 220° C. at a rate of 20° C. per minute to produce amolten formulation and held at the peak temperature for 2 minutes. Atthat time, the temperature was then lowered at a rate of 20° C. perminute until it reached the starting temperature of 60° C. The peakcrystallization temperature of the polymer was thus measured as the peakmaximum during the crystallization exotherm. The onset crystallizationtemperature of the polymer, which indicates the temperature at thebeginning of the crystallization process, was calculated using thedefault settings of Perkin Elmer's Pyris 3.81 software.

The following Table lists the haze values and crystallizationtemperatures for the plaques prepared with the mixtures of TABLE 1 (anasterisk indicates no measurements were taken for those samples): TABLE2 Haze Values and Crystallization and Onset Temperatures for InventivePlaques Haze Peak Onset Crystallization Value Crystallization Temp.Temp. Plaque # (TABLE 1)  1 8.0 113.6° C. 118.1° C.  2 8.4 113.6° C.117.9° C.  3 8.3 113.7° C. 118.1° C.  4 7.9 113.7° C. 118.2° C.  5 8.0114.2° C. 118.8° C.  6 8.0 114.0° C. 118.9° C.  7 8.1 113.9° C. 118.9°C.  8 7.9 113.9° C. 118.8° C.  9 8.2 113.7° C. 118.5° C. 10 8.3 113.6°C. 118.3° C. 11 8.4 113.6° C. 118.1° C. 12 8.7 113.1° C. 117.3° C. 137.0 * * (Comparatives) 14 8.0 114.1° C. 118.6° C. 15 10.1 112.9° C.117.1° C. 16 12.2 112.6° C. 116.8° C. 17 13.8 111.4° C. 115.3° C. 1821.5 109.2° C. 112.5° C. 19 11.1 113.3° C. 117.7° C. 20 12.0 112.6° C.117.2° C. 21 12.7 113.5° C. 118.2° C. 22 9.1 * * 23 6.9 * * 24 6.9 * *25 8.3 * *

The plaques produced with the inventive DBS mixtures, rather than theindividual DBS compounds themselves, thus exhibited comparable hazemeasurements and crystallization temperatures, all at a lower cost dueto the added amount of less expensive MDBS within the final article.

Having described the invention in detail it is obvious that one skilledin the art will be able to make variations and modifications theretowithout departing from the scope of the present invention. Accordingly,the scope of the present invention should be determined only by theclaims appended hereto.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. An additive composition forpolyolefins comprising a combination of at least two compounds,comprising: (a) a first compound comprising bis(3,4-dimethybenzylidene)sorbitol; and (b) a second compound comprising dibenzylidene sorbitol.5. The additive composition of claim 4, said composition having a ratioof said first compound to said second compound relative to saidcombination of about 1:1.
 6. The additive composition of claim 4, saidcomposition having a ratio of said first compound to said secondcompound relative to said combination of about 1:3.
 7. A polyolefin,said polyolefin further comprising a nucleating agent composition, saidnucleating agent combination composition comprising: (a) a firstcompound comprising bis(3,4-dimethybenzylidene) sorbitol; and (b) asecond compound comprising dibenzylidene sorbitol.
 8. The polyolefin ofclaim 7 wherein said first compound is provided in a concentrationrelative to said total polyolefin of about 1000 ppm.
 9. The polyolefinof claim 7 wherein said second compound is provided in a concentrationrelative to said total polyolefin of about 1000 ppm.
 10. The polyolefinof claim 7 wherein said first compound is provided in a concentrationrelative to said total polyolefin of about 500 ppm.
 11. The polyolefinof claim 7 wherein said second compound is provided in a concentrationrelative to said total polyolefin of about 1500 ppm.
 12. The polyolefinof claim 7 wherein said nucleating agent combination composition isprovided in a concentration of from about 1000 ppm to about 4000 ppm ofsaid total polyolefin.
 13. The polyolefin of claim 7 wherein saidnucleating agent combination composition is provided in a concentrationof from about 1200 ppm to about 3000 ppm of said total polyolefin. 14.The polyolefin of claim 7 wherein said nucleating agent combinationcomposition is provided in a concentration of from about 1500 ppm toabout 2200 ppm relative to said total polyolefin.
 15. An additivecomposition for polyolefins comprising a combination of at least twocompounds, comprising: (a) a first compound comprisingbis(3,4-dimethybenzylidene) sorbitol; and (b) a second compoundcomprising dibenzylidene sorbitol; and (c) wherein the ratio of saidfirst compound to said second compound is in the range between about 1:3and about 1:1.
 16. A polyolefin article comprising the additivecomposition of claim
 15. 17. The article of claim 16 wherein saidarticle comprises a random copolymer of polypropylene.
 18. A method ofnucleating a polyolefin comprising the steps of: (a) providing anadditive nucleating composition comprising at least 1000 ppm of acombination of bis(34-dimethylbenzylidene) sorbitol and dibenzylidenesorbitol; (b) providing a polyolefin formulation; (c) mixing saidadditive nucleating composition of step “a” with the polyolefinformulation of step “b” to form a resultant mixture; and (d) meltingsaid resultant mixture of step “c” to form a polyolefin having saidadditive nucleator composition applied therein.
 19. A polyolefin articlemade by the method of claim
 18. 20. A polypropylene article made by themethod of claim
 18. 21. The method of claim 18 wherein the ratio of saidbis(3,4-dimethylbenzylidene) sorbitol to said dibenzylidene sorbitol isin the range between about 1:3 and about 1:1.